In cellular systems, there is a problem of radio frequency depletion due to traffic surges. Therefore, the possibility of using an unlicensed frequency band of a 5 GHz band in cellular systems is being investigated.
A frequency band in the 5 GHz band is used in wireless local area networks (LANs). In addition, some frequency bands of the 5 GHz band are used for various types of radar and satellite communication. Therefore, in a wireless LAN access point that uses such a frequency band, it is necessary to avoid interference with various types of radar and satellite communication. Specifically, for example, an operation of dynamic frequency selection (DFS) is requested from a wireless LAN access point. The operation of DFS includes monitoring radar waves for, for example, 60 seconds.
For example, Patent Literature 1 discloses a technique in which, when one of least two wireless LA N access points that operate in a wireless distribution system (WDS) mode detects radar waves in a frequency band, the other is notified of a candidate of another frequency band, and monitoring of radar waves in the other frequency band is performed, and when radar waves are not detected, a beacon is transmitted using the other frequency band.